The invention relates to a device and a method for controlling an internal combustion engine of a motor vehicle. The inventive device and the inventive method make it possible to limit and/or regulate the rotational speed of the internal combustion engine in specific operating situations. The targeted speed reduction shall make it possible to implement preventive measures especially in operating situations that would mean an excessive thermal load on the internal combustion engine.
A variety of devices and methods already exist for the purpose of offering thermal protection to the internal combustion engine.
For example, today's vehicles have temperature indicating devices for the motor oil temperature or the cooling water temperature. In the event of critical motor oil or cooling water temperatures these temperature indicating devices allow the driver to take suitable countermeasures—for example, to stop the motor vehicle or optionally to bring the motor vehicle immediately to the automotive service center. Moreover, there exist active measures to counteract a thermal overheating to the effect that especially during stationary phases when the internal combustion engine is activated, the electrical fan units are automatically activated. However, these measures are insufficient to allow the internal combustion engine to run continuously during the stationary phase of the vehicle and/or at low vehicle speeds, when the rotational speed of the internal combustion engine exceeds the idle speed.
Such indicating and warning devices as well as active fan unit related measures known from the prior art have the drawback that they do not prevent a thermal overheating of the internal combustion engine due to misuse or the like.
Furthermore, German patent document DE 35 31 868 A1 discloses a fuel cut-off device that is intended for an internal combustion engine having a fuel supply means and that is supposed to protect the engine from excessive high speeds. This object is achieved in that the rotational speed of the internal combustion engine is constantly monitored, and on reaching a predetermined limit speed in a very high speed range, the fuel supply is cut off. Moreover, a distinction is made as to whether the internal combustion engine is operated in a loaded or non-loaded state. In the presence of a non-loaded operating state the predetermined limit value, at which a cut-off of the fuel supply is supposed to take place, is progressively reduced.
German patent document DE 33 19 025 A1 discloses a method and a device for limiting the rotational speed of an internal combustion engine. On reaching a maximum allowable limit speed, the ignition point is adjusted for the purpose of quickly limiting the rotational speed, and at the same time measures to act on the formation of the mixture are taken in order to prevent in this way the internal combustion engine from overheating as a result. Furthermore, it is proposed that the fuel supply be cut off as soon as a second higher speed limit is reached.
The object of the invention is to provide a device and a method for controlling an internal combustion engine so that the avoidance of the thermal overload on the internal combustion engine is improved even more. In particular, situations of misuse, in which a thermal overload of the internal combustion engine shall be and/or is induced, shall also be effectively counteracted.
The invention is based on the recognition that the above described devices and methods that are known from the prior art allow relatively high speeds for a prolonged period of time without providing any suitable countermeasures for a counteraction. In all cases rotational speeds just below the high limit speeds (cut-off speed) are allowed for a prolonged period of time. Therefore, in cases of continuous speeds just below the cut-off speed, thermal damage to the internal combustion engine can occur, if the excessive high speeds are present merely long enough.
The invention achieves this and other objects by exemplary embodiments of the present invention.
The device, according to the invention, comprises a control unit for monitoring and limiting the rotational speed of internal combustion engines that are designed in such a manner that after a predetermined first speed threshold an integral formation of the present speed values over time (and/or a summation of values that correlates thereto) occurs. On reaching a predetermined integral limit value, the rotational speed is automatically limited, according to the invention, to a predetermined reduced speed limit value. The predetermined first speed threshold is dimensioned in such a way that it is significantly above the idle speed and significantly below the cut-off speed (the cut-off and/or shut-off speed is (are) the maximum allowable speed, at which the engine is shut off and/or regulated for protection against mechanical damage—normally it is done by intervening in the ignition and/or the fuel supply process) of the internal combustion engine. The speed value, to which the rotational speed is limited as soon as the predetermined integral limit value is reached, is chosen in such a way that (assuming average general conditions for the outside temperature and the like) a continuous operation of the internal combustion engine without thermal damage to the internal combustion engine is possible. The speed value can be identical to the predetermined first speed threshold, but it can also be different. In particular, it can be dimensioned smaller than said first speed threshold.
The predetermined monitored speed threshold is designed advantageously so as to be variable and, therefore, can be set optimally to a variety of general conditions. In particular, (in the event that the rotational speed shall be monitored during the trip) the speed threshold is designed so as to be variable as a function of the vehicle speed and/or the engaged gear stage.
In an additional embodiment, the predetermined speed threshold is monitored exclusively in the operating mode “vehicle in the stationary mode.” Vehicle in the stationary mode is defined for the purpose of the invention as an operating mode, in which a predetermined vehicle speed is close to or equal to zero km/h (for example, v</=1 km/h) and in which the force closure between the internal combustion engine and the drive wheels is interrupted (for example, activated coupling or idle gear stage engaged). Whether the vehicle is currently stationary may be determined by a monitoring unit that monitors the state of the vehicle.
In an especially preferred embodiment, the speed range above the monitored speed threshold is divided into different speed ranges (the different speed ranges being assigned different weightings and/or weighting factors [and/or integrating rates and/or counting rates]) in such a manner that higher speeds result in a steeper rise in the integral value than lower speeds. In this way the varying load on the internal combustion engine at different speeds above the monitored speed threshold is taken into consideration.
The invention proposes, analogous to the described device, an inventive method that monitors the rotational speed of the internal combustion engine in relation to a predetermined first speed threshold in that for the period of time, during which the first speed threshold is exceeded, an integral formation of the present speed values over time is carried out, and on reaching a predetermined integral limit value, the rotational speed is automatically limited to a predetermined reduced speed limit value.
If the integral limit value is reached, then the rotational speed is regulated in a ramp manner to the reduced speed limit value by reducing the rotational speed in a linearly falling manner to the predetermined value over a predetermined period of time. The predetermined period of time is varied advantageously as a function of the predetermined operating parameters, for example, as a function of the value of the actual rotational speed that is on hand at the period of time, during which the predetermined integral limit value is reached.
Furthermore, a driver, sitting in the vehicle, is informed about the state of the integral value (and, thus, also about the thermal state of the internal combustion engine) by means of a warning signal that is generated no later than upon reaching the predetermined integral limit value. As an alternative, on reaching an integral value below the predetermined integral limit value, an early warning signal, perceivable to the driver, can already be generated. This warning can ensue, for example, by activating a warning light in the instrument panel unit, and/or a corresponding acoustic and/or haptic warning signal can be emitted.
A further development of the invention can reduce specifically the integral (and/or the incrementally growing counter value) which increases incrementally through the addition of the speed values (and/or activation of a counter) for the time segments, during which the internal combustion engine is operated above the monitored speed limit, in the presence of specific operating conditions, which reduce the input of heat and/or energy that is introduced by the internal combustion engine. As the operating conditions that reduce the thermal input, the following factors are evaluated, in particular:
the cooling, resulting from the air stream while the vehicle is travelling, on exceeding a predetermined minimum speed (for example, by monitoring the vehicle speed v, for example, v>/=50 km/h); and/or
the duration of time, during which the internal combustion engine is shut off (deactivated), and/or
the temperature of the internal combustion engine.
Other operating conditions for decrementing the integral value are provided in an advantageous manner. In particular, for availability reasons the terminal and/or signal change-over is monitored by switching off and on again the internal combustion engine (monitoring the signal state at so-called “terminal 15”), and, as a function thereof, a predetermined reduction of the integral value is initiated. This strategy has the advantage that in the event that the integral limit value was reached, the integral limit value is reduced by a predetermined amount by simply switching off and on again the ignition. Moreover, for the next operating phase of the vehicle the driver is not restricted to the reduced speed limit value, but rather can use the vehicle (at least until the integral limit value is reached again) in the conventional manner, using the normal speed range.
One embodiment of the invention is illustrated in the drawing and is described in detail below.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.